Stirring leaching

Stirring cyanide leaching is commonly used to treat materials less than 0.3 mm. It has the advantages of short leaching time, small plant area, high mechanization and high recovery rate of gold . Since the pulp is leached under stirring conditions, the concentration of oxygen in the solution is high, the diffusion is fast, the dissolution of gold is rapid, and the fine materials such as slime, clay , shale (secondary slime easily generated during grinding) are not caused. Settling affects the leaching effect. Therefore, the stirring leaching method is suitable for processing fine-grained gold-containing raw materials.

In the application of the agitation leaching method, in order to increase the recovery rate of gold, the coarse gold is usually recovered by re-election or amalgamation before cyanidation (or leaching after addition of cyanide grinding) to shorten the cyanide time. Or remove most of the gangue by re-election or flotation, and then send the concentrate to cyanide leaching to reduce the consumption of raw materials and improve production efficiency. For ores rich in fine gold particles, full mud cyanidation can be carried out after fine grinding [-0.038 mm (400 mesh) or even finer].

First, stirring and leaching equipment

The main equipment for agitation leaching is a stirred leaching tank. The stirring leaching tank has three types: air stirring leaching tank, mechanical stirring leaching tank and mixing stirring leaching tank. The flow, circulation and air distribution of the slurry in these mixers is different.

(1) Mechanical stirring leaching tank

The leaching tank agitated using propeller, impeller and turbine mixers is commonly referred to as a mechanically agitated leaching tank.

1. Propeller mixer. The propeller type agitator shown in Fig. 1 is a mechanical agitator widely used in gold selection plants today, and the foreign Devereaux type mixer is of this type. The center of the tank is filled with a slurry receiving pipe, and the pipe has a branch pipe. The vertical shaft is mounted on the bracket 5 and passes through the center of the tube 1. A propeller is mounted at the lower end of the vertical shaft. In order to prevent the ore from depositing on the propeller when the vertical shaft stops rotating, a circular cover plate is installed at the lower end of the tube 1. Therefore, this mixer can be started after the slurry is precipitated.

After the slurry is fed into the leaching tank from the launder or the feed pipe, due to the rapid rotation of the propeller, the slurry in the tank enters the pipe 1 through each branch pipe, and the air is sucked into the vortex to saturate the oxygen content of the slurry. The slurry entering the pipe 1 is pushed to the bottom of the groove when the propeller rotates, and then rises from the bottom of the groove to rise along the wall of the groove, and enters the pipe 1 again through each branch pipe to realize the circulation of the slurry. The advantage of this type of mixer is that the slurry is uniformly and strongly agitated and the air sucked into the slurry is sufficient. The cyanated pulp is discharged from the discharge pipe.

Figure 1 propeller type stirring leaching tank

1-pulp receiving tube; 2-branch tube; 3-vertical axis;

4-propeller; 5-bracket; 6-plate;

7-flow tank; 8-feed tube; 9- discharge tube

Since this mixer can be started after the slurry is precipitated, it is particularly suitable for washing and decanting of precipitated pulp. This type of mixer usually does not need to be equipped with other equipment, but sometimes it also cooperates with the blower, that is, several compressed air pipes are inserted vertically into the tank, or an air lifter is installed on the inner (outer) wall of the tank to increase the aeration of the slurry. And mixing ability.

2, axial flow mixer. It is a blender recently developed by the former Soviet Union's Quansu Nonferrous Metals Mining and Metallurgy Research Institute and has undergone semi-industrial tests. The machine (Fig. 2) is rotated by the impeller, and the slurry at the bottom of the tank is sucked into the center tube and raised to the reflector. Since the lower surface of the reflector is tapered and in a rotating state, the slurry is thrown toward the conical surface of the reflector, and is turned in a direction of nearly 90 degrees to fan the surface of the slurry in the tank. At this time, the surface area of ​​the slurry in contact with the air is large, and the slurry is filled with air. Due to the continuous rotation of the agitating paddle, the slurry is continuously sucked and discharged from the central pipe to achieve the circulation of the slurry. In order to prevent the liquid surface center funnel which destroys the suction of the impeller due to the large solid content of the slurry, a folding plate 7 is arranged on the inner surface of the suction pipe. Cyanide leaching of the slurry is carried out in this closed cycle of intensive agitation. The strong agitation of the paddles distributes the slurry evenly throughout the leaching tank and is often saturated with oxygen, which provides favorable conditions for the dissolution of gold. According to laboratory tests, when the number of revolutions of the mixer is 1500 r∕min and the slurry contains 55% solids, the dissolved oxygen concentration in the solution is 7 to 7.5 mg ∕L. The same slurry sample was subjected to a 12h comparative leaching test using an axial flow pump mixer and an air mixer. The result showed that the gold leaching rate of the axial pump mixer leaching tank was 82% to 84%, while the leaching rate of the air mixer leaching tank was only 73. %~75%.

Figure 2 axial flow pump mixer

1-tank; 2-central tube; 3-impeller;

4-axis; 5-conical reflector; 6-motor; 7-folded partition

3. Impeller mixer. The latest structure of an impeller mixer is a MIL-type impeller mixer designed by Denver, USA (Figure 3). Compared with other mechanical mixers, this mixer reduces weight by 50%, reduces power consumption by 30% to 40%, has small mechanical vibration and friction, and has a long service life. And because the impeller can make the slurry flow from the bottom of the tank to the upper part of the tank, the solid material is uniformly mixed and kept in a suspended state. It has been used in industrial production.

Figure 3 Impeller type agitation tank

(2) Air stirring leaching tank

Air agitated leaching tanks are often referred to abroad as Pachuca (or Brown Brown) air agitated leaching tanks, which use aerodynamic action of compressed air to agitate the slurry (Figure 4). The lower part of the tank is a cone of 60°. The slurry is supplied into the tank from the feed pipe, and the compressed air is supplied into the pipe 1 at the lower portion of the tank through the pipe 3, and rises in the bubble state along the pipe 1. Since the pressure of the external slurry column of the pipe 1 is greater than the pressure of the slurry in the pipe 1, the slurry in the pipe is made to rise and overflow from the upper end of the pipe 1 to realize the circulation of the slurry. After cyanidation during intermittent cyanidation operation, the slurry is discharged from the lower discharge pipe; when continuous cyanide operation is used, the slurry is continuously discharged from the upper discharge pipe.

Figure 4 Pachuca air mixing leaching tank

1-central tube; 2-feed tube; 3-compressed air tube;

4-low discharge pipe; 5-up discharge pipe; 6-slot

The air agitation leaching tank can be used without any other equipment, but it is often used in conjunction with an air lifter (see Figure 5) to enhance the aeration and agitation of the slurry.

Figure 5 Pachuca cyanide tank made in the former Soviet Union

1-tank; 2-circulator with intermediate air lifter;

3-connected fan branch pipe; 4-plus reagent solution pipe head; 5--cover observation and sampling hole;

6-disperser; 7-with cover hole; 8-pipe; 9-valve

The specifications of the air agitation leaching tank are generally 3.7 m in diameter and 13.7 m in height. The large tank sizes widely used in South Africa are Φ7.6m×16.8m, Φ6.8m×13.7m and Φ10.1m×13.7m.

(3) Mixing and stirring leaching tank

This tank is also called the rake mixer leaching tank. It is equipped with a 耙 type mixer, such as Dole type, Denver type and Warman type. This is a simple and simple mechanical mixer that is widely used in the mining sector. Since the leaching tank is equipped with a blower and/or an air lifter, it is also called an air and mechanical mixing and stirring leaching tank. Figure 6 shows a flat-bottomed round agitator with such an air lifter and mechanical weir in the center of the tank. There is also an air lifter installed around the groove, and a circular groove mixer for circulating pipes and propellers in the center of the tank.

Figure 6 搅拌 mixer leaching tank

1-air riser; 2-耙; 3-flow trough; 4-rigid shaft; 5-cross frame; 6-transmission

The slurry is continuously supplied into the tank by the feed port located at the upper part of the tank, and is layered and settled to the bottom of the tank. The concentrated slurry settled at the bottom of the tank acts on the air riser by the rotation of the crucible (1~4r∕min), and rises along the air riser under the action of compressed air and overflows from the upper part into two holes with holes. In the flow cell, the flow hole is returned to the groove. Since the launder is rotated together with the vertical axis, the slurry flowing out of the launder hole can be evenly sprinkled in the groove. The cyanated pulp is continuously discharged from the discharge port on the opposite side of the feed port to achieve continuous operation.

The ratio of the immersion tank of the rake mixer to the air agitation leaching tank has the advantages of short groove, no sediment at the bottom of the tank, fast dissolution of gold and low consumption of cyanide.

Second, the mixing cyanide operation method

The method of stirring cyanide is divided into two types: continuous stirring cyanidation and intermittent stirring cyanidation. Under normal circumstances, the continuous gold cyanide process is used in the gold-removing factories. Only the small-scale planting or processing of insoluble gold ore is used for the staged mixing cyanide, and when each leaching requires the use of a new cyanide solution. The cyanidation method was carried out by intermittent stirring. The mixing cyanidation process includes ore furnishing, adding water to stir slurry, adding reagents, controlling cyanide time, and decanting to remove tailings.

(1) Intermittent stirring cyanidation

The intermittently stirred cyanide industry is generally suitable for small mines that process ore around 10 tons per day. For large mines, it is usually done by several or even a dozen slots in parallel to increase processing capacity. The leached pulp is stored in a storage tank and filtered and washed in batches. Then add another batch of raw material to leach. In order not to cause the slurry stored in the sump to settle, it must be continuously stirred by mechanical or air.

The slurry used for stirring cyanidation usually contains 50% solids. When intermittently cyanating and washing the slurry in the same leaching tank, it is necessary to add the washing liquid after leaching to dilute the slurry to 25% solids and then wash, so the leaching tank The actual capacity should be the sum of the volume of ore sand, cyanide solution and washing liquid, and add ample capacity above the liquid level in the tank to avoid loss caused by slurry overflow.

(2) Continuous stirring cyanide

The continuous stirring cyanide operation is usually carried out continuously in 3 to 6 leaching tanks in series, which facilitates the automation of the operation process. After the slurry enters the first leaching tank and undergoes cyanidation treatment, it then flows into the second tank and the third tank in sequence. The cyanidation treatment is continued until the final leaching tank is completed and the cyanidation treatment is completed, and the slurry overflows. Send filtration and washing. Since the continuous leaching operation is continuously carried out in several tanks connected in series, the charging and unloading time is saved, and the production capacity of the equipment is also improved; and the cyanide slurry is continuously sent for filtration, and the storage tank is not required before filtration. , thereby reducing the plant area and the power consumption for mixing the slurry in the storage tank.

In order to smoothly flow the slurry from the first tank into the subsequent tanks in succession, the leaching tank should be installed in a stepped manner, and the pumping should be carried out without pumping. Under normal operating conditions, the supply and discharge of pulp in any one of the stirred tanks in series should be balanced. In any case, it is necessary to ensure that the slurry passes through the tanks smoothly, and does not affect the normal operation due to the blockage of the ore sand.

Third, technical and economic indicators of stirring cyanide

The production technical conditions and technical and economic indicators of some major cyanide gold extraction plants abroad are listed in the table below. Among these factories, Pueblo, which processes 7260 tons of ore daily, loves Landsland, which treats ore at 6000t, and Atlanta and Gusberg, which process ore below 500t. In these stirred cyanide plants, due to the nature and structural differences of the ore, the NaCN content in the slurry is between 0.025% and 0.15%, and the NaCN consumption per ton of ore is between 0.5 and 1 kg. The recovery rate of gold is more than 90%, and the highest is 97.2%.

Some foreign cyanide plants

(continued in the table)

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